Heat-shrinkable film is used to provide a label wrapping around the outer circumference of any kind of container (hereinafter, referred to as “container”), such as synthetic resin containers including polyester (PET) bottles, glass bottles, aluminum cans, or the like. In other words, a given printing is applied on the heat-shrinkable label film, which is then centrally jointed (also called as “tubed” or “seamed”) in the cylindrical shape and put on a container. Hot air is externally applied to the heat-shrinkable label film on the container, as a result of which the heat-shrinkable label film is shrunk and adhered closely to the outer circumference of the container.
Such a heat-shrinkable film that is shrunk by heat to wrap the outer circumference of a container needs to meet some requirements of different properties in consideration of the label forming process, product quality, appearance, and so forth. These properties include heat resistance, printability, gloss, transparency, adhesiveness, shrinkability, fast workability, beautiful appearance, stability in distribution, and the like. The heat-shrinkable label film can be used as a label film only if it satisfies all the requirements of these properties.
Among the known synthetic resin films, the PVC film is most suitable as a heat-shrinkable label film. The PVC film is currently in wide use as a heat-shrinkable label film, because its properties, including heat resistance, printability, gloss, transparency, adhesiveness, drawing properties, etc., are suitable to label films. However, the PVC film gives off endocrine-disrupting chemicals during its disposal process after use and thus contributes to the problem concerning environmental contamination. For this reason, South Korea and Taiwan imposes legal limitations against the use of PVC film as label film, and other developed countries are applying legal limitations or put a self-regulating system to ban the use of the PVC label film.
There have been developed some alternatives to the PVC label film: PET film and PS film. These alternative films are free from the risk of causing environmental contamination as produced by PVC film, and they are easy to collect as well as recycle. But, there still remain some problems with the PET film when used as a label film.
The PET film has good properties in terms of heat resistance, printability and adhesiveness. However, it has a specific gravity of about 1.35 which increases production cost and tends to shrink too much during thermal shrinkage. Such excessive shrinkage does not affect glass bottles or aluminum cans but makes synthetic resin containers dented or deformed. Nevertheless, an advantage of the PET film is that it has such a good heat resistance so it can be used for containers, for example such as containing fruit juice, in the high-temperature pasteurization environment normally at 98° C.
Also, the PET film is good in cold shrinkage, light-weighted with a specific gravity of about 1.05, and free from risk of excessive shrinkage. Due to its good cold shrinkage, the PET film can be used as a label film for containers to contain dairy products, such as milk, yogurt, etc. The low specific gravity enables the PET film to contribute to decrease of production costs. Without excessive shrinkage, the PET film can maintain its beautiful appearance after a heat shrinkage. On the other hand, the PS film uses an alcohol-based solvent in the place of toluene or benzene during the printing process, so it is very eco-friendly but with poor printability, creating a demand for selecting or developing an appropriate ink for good printing.
To solve the problems, the inventors of the present invention have developed a novel heat-shrinkable label film to have patents acquired as Korean Patent Nos. 926716 and 1156607 and filed an application for patent as Korean Patent Application No. 2012-25974.
The heat-shrinkable label film as disclosed in Korean Patent No. 926716 has a three-layered structure that includes a PS-based film as an intermediate layer and a pair of PET-based films adhered to either side of the intermediate layer. The three-layered film has good properties in terms of heat resistance, printability, gloss, transparency, adhesiveness, elongation properties, etc. and is thus suitable as a label film.
The heat-shrinkable label film as specified in Korean Patent No. 1156607 has a structure that includes a PS-based film formed as an intermediate layer from a PS having a specific structural formula, and a pair of PET-based films formed from a PET having another specific structural formula, where the PET-based films are adhered to either side of the intermediate layer. The label film has low specific gravity and good cold shrinkage and undergoes no excessive shrinkage.
The heat-shrinkable label film as disclosed in Korean Patent Application No. 2012-25974 consists of a PS-based film having a specific structural formula and a PET-based film having another specific structural formula so that it does not peel off during the process of printing with five or more different colors.
These label films have been used for many kinds of container. But the label films cause the user to encounter a problem in collecting the container for recycling purpose. For the purposes of recycling, for example, the containers mostly formed from PET will necessarily need to remove the label film, which were shrunk and adhered firmly to the containers. The reason for removing the label film from the PET containers lies in the fact that the label film typically consists of a PS component which differs from PET and contains a printing in different color inks, causing contaminations when mixed with the clear PET container hus will reduce the product value of the PET containers for recycling. For these reasons, the Korean government encourages the development of label films easily removable with water in order to easily collect and dispose the label films and efficiently collect the PET containers.
When the PET container with a label film is pulverized and dipped in water for removal of the label film, the PET pieces which is light-weighted due to a specific gravity of PET about 1.35 will sink to the bottom of the water tank, while the label pieces having a specific gravity less than 1 will float on the water and thus easy to remove. In this manner, the PET pieces at the bottom of the water tank can then be easily collected and recycled. For this separation process, saline water containing salt can be used to remove the label film. In this case, however, there is a problem to wash the PET pieces to eliminate the saline water, resulting in a burden of expense and environmental problems.
The heat-shrinkage label film of the present invention is developed to solve the problems described above, contriving a label film floating on water because of its low specific gravity of less than 1. The PET container using the label film of the present invention is collected, cut into pieces in proper size with a cutter and sent to a water tank. The PET pieces will sink at the bottom of the water tank and the pieces of the label film will float on the water. The pieces of the label film are then removed and disposed, while the PET pieces are collected for recycling.